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PILE DYNAMIC TESTING USING PILE DRIVING ANALYZER (PDA)

Dynamic Formulae which calculate pile bearing capacity using the “set” of the pile due to each hammer blow at the final stage of driving are now largely discredited as a means of predicting the resistance of piles to static loading. On the contrary, the use of wave propagation theory to analyze strain and acceleration measurements during pile driving or impact waves (for bored piles), has enjoyed a wide support all over the world.

The Pile Driving Analyzer (PDA) measures strain and acceleration using strain transducers and accelerometer bolted near the top of the pile. The PDA converts the measured signals to force and velocity for use in its digital processor. Using closed form solutions to wave propagation theory, the PDA then solves for activated soil resistance, maximum pile stresses during driving, pile integrity and hammer performance.

In the last 20 years, thousands of piles in thousands of construction sites in many countries have been dynamically tested using PDA. The results have been correlated with data from several static load tests. Dynamic Pile Testing has also been officially recognized in ASTM Standard D 4945-89.

In contrast of time-consuming, space taking and costly static load testing, dynamic testing using PDA only takes a few hours to complete at a fraction of the cost, thus more piles can be tested at less time. Aside from that, PDA testing can be performed during driving or re-strike (re-drive). The system has also been used successfully for cast in situ (bored) piles, where impact waves are generated by dropping suitable mass to hit the piles.

HIGHLIGHT!

Dr. Indrawan — our Principal Engineer, demonstrating how to operate the first generation of PDA instrument in 1990.

CAPWAP

The CAPWAP computer program determines the soil resistance parameters which produces the best match between measured and computed force and velocity at the pile top. The latest version of CAPWAP uses continuous elements to model the pile and soil system.

If used to reanalyze a PDA result on test piles, CAPWAP provides invaluable information to optimise the pile length and pile dimension. Using CAPWAP to match PDA result on production/used piles confirms the piles capacity prediction using the Case Method (PDA) as well as provides a host of other useful information such as bearing graphs and simulated load-settlement curves, which are not produced during the time of driving by PDA. CAPWAP’s prediction has been compared with static load tests data and the excellent correlation is found.